Hair- and body-cleaning agents usually contain a preservative for effective protection of the agent against an attack by microorganisms.
A preservative for hair- and body-cleaning compositions must satisfy conflicting requirements. The preservative should be well compatible physiologically and dermatologically on the one hand and should have a germ-inhibiting or even germicidal effect on the other. However, these two requirements are usually difficult to combine with each other.
For example, the following conventional preservatives are commonly used in hair- and body-cleaning compositions: formaldehyde, 5-bromo-5-nitro-1,3-dioxane, p-hydroxy-benzoic ester, 2,4,4'-trichloro-2'-hydroxy-diphenyl ether, 5-chloro-2-methyl-3-isothiazolone, 2-methyl-3-isothiazolone, and 2-bromo-2-nitropropane-1,3-diol.
Recently a number of preservatives, as for example, formaldehyde and 2-methyl-3-isothiazolone, have been suspected of not being sufficiently compatible. It is known that aldehydes and phenols, which have a preserving effect, react with proteins and interact with them in a denaturating manner. In the case of aldehydes there additionally exists the risk of sensitization.
In the literature formic acid and benzoic acid have been described as preservatives. However, formic acid was not used in hair- and body-cleaning compositions heretofore and benzoic acid alone shows no adequate preserving effect in low concentrations while it has an undesired keratolytic effect when applied in high concentrations. Formic acid has an unpleasantly pungent odor and an intensely corrosive effect. A further reason why formic acid is not applied as a preservative in hair- and body-cleaning compositions is that it has a low pH value at which there occurs a hydrolysis of the alkyl ether sulphates conventionally applied as surfactants in hair- and body care compositions.